1. Field of the Invention
The present invention relates to an automatic sheet transporting apparatus configured to separate and transport sheets stacked on a feed tray portion one by one to a discharge tray portion, and an automatic document scanning apparatus having this automatic sheet transporting apparatus and a scanning device configured to scan an image of a transported document at a scanning position. Also, the invention relates to an automatic sheet transporting apparatus configured to be capable of guiding a succeeding sheet or document to be discharged in between a sheet or document already discharged on a paper discharge tray portion and the discharge tray portion and then transporting the succeeding sheet or document smoothly, and an automatic document scanning apparatus having this automatic sheet transporting apparatus.
2. Description of the Related Art
In general, in an image scanning apparatus which is capable of scanning an image surface of a transported document, an image scanning device such as a CIS (Contact Image Sensor) or a CCD (Charge Coupled Device) unit is arranged on a lower surface of a document passage transparent panel (glass plate). An automatic document transporting apparatus provided in a lid-type cover member, which is openable and closable with respect to an upper surface of the document passage transparent panel, separates and transports a plurality of documents stacked on a paper feed tray portion one by one to the document passage transparent panel, then the image scanning device scans the image surface of the transported document, and then the document is discharged on a paper discharge tray portion.
A document transporting path in this case is formed into a U-shape extending from the paper feed tray portion for documents arranged on the upper side to a paper discharge tray portion arranged on the lower side via a document scanning position, which is provided in an automatic document scanning apparatus of an upper paper feeding system as shown in JP-A-2003-76074, and a type formed into an U-shape extending from the paper feed tray portion for documents arranged on the lower side to the paper discharge tray portion arranged on the upper side via the document scanning position, which is provided in an automatic document scanning apparatus known as a lower paper feeding system as shown in JP-A-2005-247575.
In the automatic document scanning apparatus of the lower paper feeding system, a plurality of documents are stacked with the image surfaces down on the paper feed tray portion, and the documents are separated and transported one by one from the lower most document to a scanner. Then, in the scanner, the documents are transported with the image surfaces opposed to an upper (front) surface of the document passage transparent panel and, when the documents are discharged to the paper discharge tray portion via the U-shaped document transporting path, are stacked thereon with the image surfaces up.
In the case of the automatic document scanning apparatus of the lower paper feeding system, when the heightwise position of a nip of a paper discharging roller pair arranged at a terminal end of the U-shaped document transporting path is higher than an upstream end of the paper discharge tray portion in terms of discharging direction, the succeeding documents are stacked on the upper surface of the previously discharged documents.
Accordingly, the order of documents stacked in the paper discharge tray portion with the image surfaces up is completely reverse from the order of the documents stacked in the paper feed tray portion. In order to arrange these documents in the original order, it is necessary to manually rearrange the document order, which may take a great deal of time and effort.
Therefore, in JP-A-2005-247575, the heightwise position of the nip of the paper discharging roller pair arranged at the terminal end of the U-shaped document transporting path is set to be lower than the upstream end of the paper discharge tray portion in terms of the discharging direction so that the succeeding documents discharged therefrom are guided to the underside of the previously discharged documents (this is referred to as “slip” under or in). Consequently, the documents are stacked on the paper discharge tray portion in the same order as the order of the documents stacked in the paper feed tray portion (hereinafter, referred to as “same order stacking”).
However, if the number of documents stacked in the paper discharge tray portion is increased, the weight of the stacked documents is also increased. Then, the subsequently discharged document is subjected to increased frictional resistance when being transported further after having slipped between the previously discharged documents stacked in the paper discharge tray portion and the paper discharge tray portion. Consequently, even though the subsequently discharged documents can be slipped in between the paper discharge tray portion and the previously stacked documents, the slipped documents cannot be transported smoothly any longer.
In contrast, in JP-U-H07-8356, in the automatic document scanning apparatus of the upper paper feeding system, documents placed on the paper feed tray portion with image surfaces down are scanned by the scanner arranged on the inner diameter side of the document transporting path in the U-shape, and are discharged on the paper discharge tray portion arranged at a lower level than the paper feed tray portion with the image surfaces up. In this type as well, a configuration in which an angular protrusion in lateral cross section is provided on the upstream end of the paper discharge tray portion in terms of the discharging direction so as to lift the rear end side of the discharged documents upward, and a freely rotatable roller is provided on the surface of the angular protrusion is proposed as a device for guiding the subsequently discharged documents smoothly on the underside of the documents discharged previously in order to stack the documents in the same order. In this configuration, the resistance that the subsequently discharged document is subjected to may be reduced when slipping in between the previously discharged documents and the angular protrusion. Consequently, the subsequently discharged documents can be transported more smoothly.
However, when the number of documents stacked in the paper discharge tray portion is increased, the frictional resistance between the documents previously discharged and stacked and the paper discharge tray portion is increased on the downstream side of the paper discharge tray portion in terms of the discharging direction (the position where the above-described roller is not arranged). Consequently, after the subsequently discharged document has slipped in between the paper discharge tray portion and the previously stacked documents, the document cannot be transported smoothly any longer. Therefore, there is a problem such that the allowable number of documents to be discharged and stacked cannot be increased.